The antibiotic vancomycin alters the gut microbiome in a way that can help prime the immune system to more effectively attack tumor cells after radiation therapy.
In a new study, researchers found that giving a dose of the common antibiotic not only helped immune cells kill tumors that were directly treated with radiation, but also kill cancer cells that were further away in the body.
The research was conducted by a team at the Abramson Cancer Center of the University of Pennsylvania.
More than half of all patients with solid tumors undergo radiation therapy at some point during their treatment.
In recent years, many studies have shown that giving patients higher doses of radiation over the course of fewer treatments—called hypo-fractionated radiotherapy—can induce a stronger immune response in patients.
In addition, hypo-fractionated doses have the ability to impact other tumor cells in the body that weren’t directly treated with radiation. This is known as the abscopal effect.
The study shows that common antibiotic vancomycin seems to boost the effectiveness of the hypo-fractionated radiation itself on the tumor site while also aiding the abscopal effect, helping the immune system fight tumors away from the treatment site.
The team chose vancomycin for a few specific reasons. First, it mostly targets gram-positive bacteria, making it disruptive to the gut microbiome.
Second, it’s a large molecule, which means it stays in the gut and does not circulate to the rest of the body the way other antibiotics do.
The fact that it is not systemic limits the impact it has on the rest of the body’s microbiome.
While researchers used melanoma, lung, and cervical cancer models for this work, they note the approach could have implications for a wide variety of cancer types.
This study also builds off the team’s previous research, which showed a similar effect in T cell therapies, meaning it adds to a growing body of evidence.
The researchers are planning a phase 1 study to translate this approach into the clinic.
One author of the study is Andrea Facciabene, Ph.D., an associate professor of Radiation Oncology in Penn’s Perelman School of Medicine.
The study is published in The Journal of Clinical Investigation.
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